NEW YORK — Robert Reich began his career thinking it was possible, inevitable even, that his generation would change the world. He was a summer intern under Robert Kennedy then, just 20 years old, and he was already certain his life would be spent fighting, one way or another, for a more equal society.

Reich is now 67. And while he remains an optimist, he is also clear-eyed about the fact that America is less equal today than it has been since before the Great Depression, with the top 1 percent holding onto more than 35 percent of the nation’s total wealth, while the bottom 50 percent has just 2.5 percent. How it got to this point is what Reich sets out to explain in a new documentary, “Inequality for All,” in which he describes and critiques a state of affairs he has been trying — and, as he himself acknowledges, failing — to change his entire life.

“You know, I’ve written 13 books, I’ve been in a president’s cabinet, I’ve run for office [including a failed 2002 bid for governor of Massachusetts],” Reich said during a recent interview in Manhattan. “I’ve run out of options!” he added, jokingly. “This is the last hurrah. If this doesn’t educate the public, I give up.”

The documentary, which opens Friday and was conceived and directed by Jacob Kornbluth (“The Best Thief in the World,” “Haiku Tunnel”), is being billed as “ ‘An Inconvenient Truth’ for the economy” — a wake-up call, in other words, as well as a call to arms. In it, Reich argues that a more equal society would benefit everyone, including the very wealthy, because a strong economy requires a prosperous middle class. And as he makes his case, a narrative takes shape around him that traces his life — from growing up as a shrimpy kid in South Salem, N.Y., to becoming labor secretary under President Bill Clinton to driving a Prius and giving rousing lectures while standing on a wooden box to compensate for his for his 4-foot, 10-inch frame.

Reich, who has also taught at Harvard’s John F. Kennedy School of Government and at Brandeis, said he was initially reluctant to make the film about himself, before finally giving in to Kornbluth’s urging. “My biography is utilized by Jake to bring the viewer in, emotionally,” Reich said. “And while Jake convinced me that it’s necessary, I was not always comfortable with it, to tell you the truth. But I now see it. Jake convinced me that viewers need to be connected to a messenger.”

Part of the motivation for this, according to Kornbluth, was that he wanted to avoid making yet another documentary that hit viewers over the head with a rousing but ultimately artless political message — a form that’s proliferated over the past decade or so, arguably starting with Michael Moore’s “Bowling for Columbine.” “I resist anything that feels didactic,” Kornbluth said. “When the idea to make a film about income inequality came to me, I was desperate that it not be just part of what I consider to be the issue-oriented film parade.”

When he first approached Reich about doing the movie, Reich assumed it wouldn’t be that different from being on TV, something he had done many times over the years. But the project turned into a deep collaboration — one that Kornbluth said turned briefly contentious when it came time to have the “difficult conversations” about integrating Reich’s personal story into the structure of the movie.

The emphasis placed on Reich’s lifelong campaign against inequality has an unintended effect: Though the movie ends on an optimistic note, with Reich telling an auditorium full of his young students at Berkeley to go out and do their part in making the world a better place, it’s hard not to think about the fact that he himself is proof of just how difficult it is to achieve real change. After all, this is a guy who, unlike most of us, actually had real political power as a member of Clinton’s cabinet — but, as the film makes clear, even then he found himself frustrated by how little he could get done. During one particularly powerful moment, Reich admits that he occasionally asks himself whether he has been a complete failure.

“I mean, I’m very honest,” Reich said. “I have been working on this issue in one way or another for 35 years, since the trend began. And there are times when it’s discouraging.” Working in the White House, he added, made him realize that no matter who’s in charge, the trend-lines he’s devoted his life to pushing against will never be reversed unless a well-organized and disciplined social movement exists to put pressure on Washington. In this light, the images of Occupy Wall Street demonstrations and Tea Party protests that appear in the film can seem like lost opportunities — scenes of political passion that only very rarely gets channeled into true action, and which has, in recent years, proven woefully insufficient in leveling the American playing field.

During the making of the movie, Kornbluth watched footage of Reich making his argument about the pernicious effects of economic inequality over and over again. “The message stays the same,” Kornbluth said. “And it’s a little bit shocking to think about how long he’s been fighting for this stuff, in so many different ways — in the cabinet, as a lecturer, on TV, as a pundit writing books, and to think that right now, after all this time, we’re at this extreme. . .” But Kornbluth sees this in a positive light. “It’s inspiring to think about someone fighting that long, and of course it would have been a very different movie if he had fought this fight already and won.”

It’s worth asking what “winning” would really mean in this context. The problem, after all, did not appear overnight, and it won’t go away overnight. This is why Reich is hoping the film reaches young people, in particular. “They’re the future,” he said. “They’ve got to understand this because they’re inheriting this mess.”

And while the students in his classroom look sincerely moved in the film’s closing scene, Reich seems realistic about his movie’s power to inspire the kind of political confidence in today’s youth that he and his friends apparently felt during the ’60s.

“Unfortunately, younger people today don’t have any experience of efficacy, of agency,” Reich said, sadly. “They’ve seen a system that has gone from bad to worse.”